Hello,

thanks for your help in advance,

In my truck,
1987 Ranger STX 4x4 with a 5.0 from a 84 Mercury Grand Marqui,

I have had problems with my electric fuel pump. losing power. Happens about every 4 months. I have pulled the some of the wiring harness apart and tried to trace it but still no luck.

Any way on to the solution I am thinking about is to direct wire the pump to the battery, have a inline fuse of course but then to run the ground to an oil pressure switch. so when there is oil pressure the fuel pump runs and if the oil pressure drops for some reason the fuel pump will shut off.

Reason's for doing this would be that way I don't have wire the pump to run with the Key on wiring that mess up on me every 4 months and always in crappy weather.

#2 reason is then in the winter I like to leave the truck run when doing errands but have come back to it numerous times and she's not running any more but the fuel pump is still pumping away.

my question is due Oil pressure switches like thisEbay Link when there is oil pressure due they provide Path to ground/negative. and then when there is not oil pressure due they Open so there is not a path to ground/negative.

or due that work in the reverse of how I am thinking? Pressure = Open connection,
No pressure = Connection to ground/negative?

I don't know but I have the truck all apart and now is the time to add this in instead of when the Cab is back down on the frame

 

You may have a flakey fuel pump relay, have you checked that?

If your engine is carburated then ignore the rest of this post.

I can't answer your questions about the operation of the switch, but I think the type of setup you're considering won't work if your engine is fuel injected. You need fuel pressure in the fuel rail to start the car, meaning the fuel pump has to turn on for a couple of seconds to build up the pressure before the engine is started. You don't have any oil pressure until the engine is running, so your fuel pump won't be able to build up that pressure if it's connected to the oil pressure switch.

 

Yes, I agree, you will have to crank for a long time to build up enough oil pressure to close the oil pressure switch, to start the fuel pump so it will run.
One other problem, the contacts in the oil pressure switch are not designed to carry the current the fuel pump pulls....

 

I am runnig a low pressure pump with a 2 barrel carb.

also I was thinking to wire up a bypass switch that I could also manual turn on the pump and turn it off If I had 2. this would not leave me stranded on dark and cold night.

so now I guess I will look into the amp draw of my fuel pump and find out what the oil pressure switch can hold

thanks again sublime out

 

Hmm. No mechanical fuel pump on that engine?

A switch might be a good idea. Hide it somewhere and it will also help with theft prevention.

 

Thanks for the replays so far.

the Mechaninal pump wont work since the steering box is in the way and I am pretty sure the block is not drilled out for it either. I will check on that tomorrow.

ah the joy of upgrading from the v6 to the v8. motor swap's are so much fun
but slowly and surely I am getting the bugs worked out of it. Right now I have it apart to put in a manual transfer case instead of the flaky electric one that only works when it wanted to.

and since I have it all tore down thought it would be a good time to work on my fuel problems that I have.

thanks again sublime out